1. Field of the Invention
The invention relates to a video surveillance system, and more particularly, to a dynamic calibration method for a single and multiple video capture devices.
2. Description of the Related Art
For a surveillance system with a plurality of pan-tilt-zoom (PTZ) cameras, cameras may pan, tilt, or zoom from time to time to acquire different views of the monitored scene. However, when a camera pans or tilts, its extrinsic parameters change accordingly. For this type of surveillance systems, how to accurately and efficiently recalibrate the extrinsic parameters of a plurality of PTZ cameras has become an important issue.
Up to now, various kinds of approaches have been developed to calibrate static camera's intrinsic and extrinsic parameters. For example, an off-line method has been proposed to find the relationship between the realized rotation angle and the requested angle so that they could control a PTZ camera to keep tracking moving objects in the monitored scene. (A. Jain, D. Kopell, K. Kakligian, and Y-F Wang, “Using stationary-dynamic camera assemblies for wide-area video surveillance and selective attention,” Proceedings of IEEE Conf. Computer Vision and Pattern Recognition, vol. 1, pp. 537-544, June 2006). Even though the error is corrected via the off-line training for each rotation request, yet it is still difficult to estimate the camera pose for each camera. Further, this method only demonstrated the dynamic calibration of a single PTZ camera, but not the calibration among a plurality of PTZ cameras. Another method utilized the marks and width of parallel lanes to calibrate PTZ cameras. (K.-T. Song and J.-C. Tai, “Dynamic calibration of pan-tilt-zoom cameras for traffic monitoring,” Proceedings of IEEE Transactions on Systems, Man and Cybernetics, Part B, vol. 36, Issue 5, pp. 1091-1103, October 2006). Although this method is practical for traffic monitoring, it is not generally enough for other types of surveillance systems.
Moreover, a dynamic camera calibration method with narrow-range coverage has been proposed. (C. T. Huang and O. R. Mitchell, “Dynamic camera calibration,” Proceedings of Proc. Int. Symposium on Computer Vision, pp. 169-174, November 1995). For a pair of cameras, this method performed the correspondence of feature points on the image pair and used coplanar geometry for camera calibration. Still another method utilized plane-based homography to determine the relative pose between a calibrating camera and a projector. (B. Zhang, “Self-recalibration of a structured light system via plane-based homography”, Proceedings of Pattern Recognition, vol. 40, Issue 4, pp. 1168-1377, April 2007). Nevertheless, this method requires a corresponding feature point and a structured light system to generate plane-based calibration patterns.
The aforementioned methods required corresponding feature points and/or special calibration patterns. However, to dynamically calibrate a plurality of PTZ cameras, calibration patterns and landmarks are not always applicable since they may get occluded or even move out of the captured scenes when cameras pan or tilt. On the other hand, if using the correspondence of feature points, we need to keep updating the correspondence of feature points when cameras rotate. For a wide-range surveillance system with many PTZ cameras, the correspondence of feature points cannot be easily solved.
Therefore, to solve the aforementioned problems, the present invention proposes a novel dynamic calibration method to improve the efficiency and feasibility for the calibration of video capture devices.